1. Field of the Invention
The present invention relates to a photometric system structure which is used in a printer section of a printer processor and which enables a prism and a mirror both to be used to obtain photometric light from light passing through a photographic film to measure the density of the photographic film or the like.
2. Description of the Related Art
In a printer section of a printer processor, light emitted from a light source passes through a negative film, and an image on the negative film is printed onto a photographic printing paper through a lens system.
Here, density correction and color compensation are effected in order to select a printing condition, photometric light is obtained from the light passing through the negative film and the obtained photometric light is received by a sensor such as a CCD.
Thus, when the negative film is a 35 mm film, a prism is disposed between a lens system on an optical path and the negative film. The prism is used to allow a part of the light passing through the negative film to be made incident on the lens system and also allow the remaining part of the light to be irradiated to the sensor as the photometric light.
On the other hand, when the negative film is a Brownie film or the like, a lens system corresponding thereto is used in place of the above-described lens system. Since the lens system corresponding to a Brownie film is of a large size, a mirror, not a prism, is used to obtain photometric light. Before the lens system is mounted, the mirror is positioned between the negative film and the photographic printing paper and causes the light passing through the negative film to be reflected, as the photometric light, toward the above-described sensor. After a printing condition is selected by the sensor which detects the light, the mirror is withdrawn from the optical axis, and thereafter, the lens system is mounted and an image is printed onto the photographic printing paper.
Although the optical axis of the photometric light obtained by the prism and the optical axis of the photometric light obtained by the mirror are disposed in the same direction, the prism and the mirror have different optical-path lengths. A correction lens is required to correct the different optical-path lengths.
The correction lens is conventionally provided between the sensor and the prism or the mirror and is moved and adjusted on the optical path such that the same optical-path lengths are obtained when the prism is used and when the mirror is used. Further, when the prism is used, the correction lens is mounted between the sensor and the prism, and when the mirror is used, the correction lens is removed from its mounted position. Thus, the same optical-path length is obtained when the prism is used and when the mirror is used.
Each time the lens system for the prism and the lens system for the mirror are replaced by the other, it is necessary to separately adjust and move the correction lens, or to mount or remove the correction lens between the sensor and the above-described optical system, thereby resulting in complicated operation.